The use of borate esters of hindered phenols, i.e. phenols in which both ring positions ortho to the hydroxy group have been substituted by bulky hydrocarbyl groups, is known in the art for their antioxidant and antifatigue properties in a variety of products including lubricating oils, greases, and fuels. U.S. Pat. No. 3,347,793, for example, teaches certain 2,6-di-t-alkylphenyl borates as oil additives. U.S. Pat. Nos. 3,356,707, and 3,359,298 disclose similar compositions.
The use of arylamines, such as alkylated diphenylamines, p-phenylenediamines, have been well known for their antioxidant properties in a variety of products including polymers and lubricants.
The use of hindered phenols containing a polar amine-substituent with desirable surface-active properties has proven valuable in many types of industrial oils; antirust protection is improved, and inherent dispersancy characteristics help lengthen maintenance periods by inhibiting the deposition of harmful deposits. A good example is Ethanox 703 (2,6-t-butyl-.alpha.-dimethylamino-p-cresol) commercially available from Ethyl Corporation.
It has now been found that the use of the novel borate esters of amine-containing hindered phenols in accordance with this invention provide exceptional antioxidant activity, with the multifunctional potential of antifatigue, antirust, and antiwear properties.